The present invention relates to code division multiple access (CDMA) systems with multi-user detection (MUD) capabilities, where the capacity of the system is limited by non-cancelled intra-cell interference, non-cancelled inter-cell interference and interference associated with the noise floor.
In CDMA systems, one of the factors that limits the capacity of the system is interference. In general, these systems try to generate as little interference as possible. Power control is one approach that is commonly used in order to maintain the interference limits as low as possible. Nevertheless, when a CDMA system attempts to support many users, even if the transmission power is being controlled, the levels of interference may not be acceptable.
The concept of CDMA uplink (UL) pole capacity has been widely used for evaluating when a system is becoming congested. This concept is based on the exponential growth of interference caused by a CDMA system, i.e. all interference above the noise floor. The interference caused by a CDMA system is made up of intra-cell interference and inter-cell interference. Intra-cell interference is interference generated in a cell that is occupied by a user. Inter-cell interference, in contrast, is interference generated from all sources outside of the cell in which the user is located. The pole capacity is the theoretical maximum capacity assuming the mobiles have infinite available transmitting power. The actual capacity is typically a fraction of the pole capacity. Although the concept generally applies to any point-to-multipoint CDMA system, the use of a MUD in the receiver that cancels some of the intra-cell interference varies the principle on which the concept is based thereby rendering the concept not applicable.
A method is therefore needed for evaluating congestion in CDMA systems having MUD capabilities.